1. Field of the Invention
This invention relates in general to video recording apparatus, and in particular to apparatus for use in replaying segmented video at various speeds, e.g., fast or slow forward, or fast or slow reverse, or stopped, as may be required for the editing of video program material recorded on magnetic tape.
2. Description Relative to the Prior Art
The editing of video program material recorded on magnetic tape is a difficult job. Although there are some video recorders which record discrete fields or frames of video information across the width of a magnetic tape, most video recorders record segmented fields. Quadruplex recorders and many helical recorders fall into this category: A quadruplex recorder lays down 16 widthwise tracks, each track of which corresponds to 16.2 video lines, to record a single video field; a helical recorder such as the BCN recorder, produced by Robert Bosch, GMBH, Fernseh Division, Darmstadt, West Germany, lays down five slantwise tracks, each track of which corresponds to about 50 video lines, to record a video field. Because of the segmenting of the video field information, the recorder tape drive--say for purposes of program editing, etc.--cannot be run at any, or no, speed without employing elaborate, and expensive, buffering equipment, viz, an editing machine. One cannot merely plug, say, the playback signal of a variable tape speed quadruplex recorder into a monitor and get a meaningful display on the monitor, unless the quad tape is replayed at its record speed. Were recorded-on quadruplex tape to be stopped, the play heads would repeatedly scan the same 16.2 recorded video lines with attendant tearing apart of the image display; were quadruplex tape to be run, say, at high speed, the quadruplex heads would "hopscotch" from segment to segment of different fields, again with attendant tearing apart of the image display.
A current practice in the editing of magnetic tapes is to transfer to and store taped program material, along with frame time/program identifiers in a random access memory, say as in the CMX Editing System of CBS/Memorex. Such an editing system employs 20 disc recording surfaces, each capable of storing five minutes of skip field (or 21/2 minutes of full frame) "2 mHz" video information; and monitor apparatus capable of displaying frame and time information. Selectively, editing decisions for splicing tapes, for lap-and-dissolving scenes, etc. are made by viewing the monitor.